The present invention relates generally to casings used for packaging food products such as sausage and the like. More particularly it is concerned with a non-viscose-bonded fibrous base web used in making reinforced casing, and a method of making the non-viscose-bonded fibrous base web.
Heretofore it has been the practice to make reinforced films, tubing, casings or skins for food products and the like by the encasement of bonded fibrous base papers or substrates in a film forming material. The substrate must have good absorptivity to provide for proper penetration of the encasing material. In order to withstand the treatment conditions at the time of encasement, the substrate must possess substantial wet and dry strength. Furthermore, when a caustic encasing medium such as viscose is used, the substrate must have sufficient caustic strength to enable it to retain its structural integrity during casing-forming operations. Heretofore substrates of this type frequently have been prepared by bonding a preformed and dried paper or fibrous base web with a dilute (1%) viscose solution followed by the steps of drying, regenerating the cellulose, washing and redrying. This bonding operation using the dilute viscose solution is sufficient to impart to the substrate adequate caustic resistance, and to allow the substrate to retain its porous, absorbent characteristics in order to result in complete impregnation and encasement by the concentrated viscose solution. Typically the casing-forming operation includes the steps of forming the substrate into a cylindrical tube, impregnating and encasing the substrate tube with a highly caustic viscose solution, regenerating the impregnate with acid, washing to remove excess acid and viscose, and drying the final reinforced film or casing. This process is set forth in greater detail in U.S. Pat. No. 3,135,613, Underwood, entitled "Impregnated Paper Webs and Method of Making Sausage Casing Thereof", thus clarifying the sequential evolution of the base web through the bonded substrate phase and then into the reinforced casing.
The casings produced in the manner set forth possess sufficient elasticity and burst resistance to be particularly well suited for enclosing meat and other food products that are injected into the interior of the tubes under pressure. Furthermore, they are sufficiently thin to allow proper drying of the tube during manufacture, and to provide for good through-sheet viscose penetration under rapid encasement operations, favorable shirring characteristics, and acceptable clarity of appearance. The viscose-bonded, viscose-encased casings thereby provide firm, uniform enclosures for well known products such as sausage, bologna and the like as well as other food products.
However, due to the environmental concerns associated with the use of viscose, various patents subsequent to the aforementioned U.S. Pat. No. 3,135,613 are directed toward the use of alternative materials for bonding the paper webs to provide appropriate casing substrates. In selecting bonding materials other than the commercially employed acid-regenerated dilute viscose, it is important that the bonding materials meet both the processing and performance requirements of the food casings to be produced therefrom. The substrate must retain its porous, absorbent characteristics in order to permit complete impregnation and encasement by the concentrated viscose solution. This is necessary in order to impart the required specific physical properties to the finished tube which make it an effective casing, or other end-use product. These physical properties include adequate strength and tube stretch during the stuffing, cooking and curing operation to ensure that the casing expands (or shrinks) to the required diameter, necessary clarity of appearance and a lack of unsightly artifacts. In addition, the initial base substrate must be thin enough to allow for proper drying of the tube during manufacture and for sufficient through-sheet viscose penetration under dynamic conditions. The substrate also should result in a casing having favorable shirring and other convertibility characteristics.
The characteristics described above have been embodied in the traditional viscose binder. The alternate binders that have been tried, however, have met with varying degrees of success. While certain of the chemical characteristics of viscose have been mimicked by alternative binders, viscose has thus far been unique in the magnitude of its three-dimensional shrinkage during regeneration, producing a uniquely thin sheet while maintaining its extensibility and other above-mentioned characteristics without further treatment. The use of a non-viscose-bonded substrate which is generally thicker than the conventional viscose-bonded substrate can result in poor viscose penetration under rapid encasement processes as well as poor shirring characteristics of the final casing, and can lead to drying problems and/or the appearance of artifacts on the casing. Furthermore, when alternative binders are used, in order to compensate for the lack of shrinkage and the resulting thicker paper product, it may be necessary to reconfigure or modify the equipment that is used during encasement, or to alter the encasement process itself such as by decreasing viscose viscosity or increasing dwell times, the latter reducing productivity. Furthermore, a casing formed from a viscose-bonded sheet has a characteristic high extensibility (as the tube is being expanded) which generally cannot be matched by alternate bonding systems. Thus, a reconfiguration or modification of equipment used in stuffing operations may be required to accommodate a non-viscose-bonded casing, or, in order to expand to the same final diameter as the naturally stretchy viscose-bonded casing, the paper might have to have a larger initial width than a viscose-bonded casing paper. Such reconfiguration or modification of converting equipment can be expensive and inconvenient, requiring shut-down of operations.